The use of bulk polygonal packs or round drums containing large quantities of reverse wound aluminium welding wire (in some cases up to as much as 500 kgs) is becoming increasingly popular since it offers the advantage of great savings thanks to a reduced pack changeover downtime and a higher productivity. The ability to avoid unwanted weld interruptions in some applications like the production of vehicle components and automotive parts, is extremely important because stoppages in the middle of the automated weld process can cause cracks, weld defects, mechanical failures with consequent costly aftermarket product liability issues. A good weld with no defects or imperfections is absolutely necessary in order to prevent subsequent equipment failures.
Unwanted production interruptions can offset the advantages of the so-called “lean manufacturing process” that relies on the optimization of the supply flow in sequential steps of production.
The industry today, and in particular the automotive industry, is increasingly using aluminium welding wires for many applications, since aluminium has the advantage of being a resistant, fairly strong, corrosion-free metal but also much lighter (approximately three times lighter) than steel; vehicles with less weight bring relevant fuel savings.
More and more manufacturers are choosing bulk containers with large quantities of twist-free reverse wound welding wire in combination with high performing low friction guiding liners with rolling elements inside.
Aluminium wires are however very soft and can easily be deformed by friction or attrition in particular when the wire during payout is forced to scratch against the inner edge of the wire retainer. Deformed wires can cause serious weld defects that would either require repair where possible, or in the worst case scenario, the inevitable scrapping of valued parts because of their non conformance to the desired quality standards.
This problem has been known for a while and several prior art attempts have been made to solve it.
Barton and Carroscia in U.S. Pat. No. 7,398,881 propose a rigid retainer ring with embedded pockets of different shape and density in order to help reduce the overall retainer weight. The attempt to generate some weight relief is obvious but notwithstanding the pockets the retainer maintains its rigidity, and this could still deform soft aluminium wires (like, but not limited to, the grade AWS 4043) in the commonly used thin wire diameters like for example 1.20 mm.
Again Carroscia in U.S. Pat. No. 7,410,111 describes, as a possible solution, the cut out of entire retainer sections in order to decrease the retainer plate weight by as much as 50% of its overall weight. This plate however is rigid and it can still deform the wire during payout; additionally this particular embodiment comes with the risk that the wire coil under the retainer can become excessively exposed to air contamination and oxydation.
Edelmann and Zoller in EP 2 354 039 also try to address the problem of the possible impact of a heavy retainer on the wire coil and disclose a retainer exerting a contact pressure on the wire spool for maintaining the spirals of the spool which is between 10 and 25 N/m2. This retainer with a claimed thickness of up to 15 mm has a significant degree of rigidity.
Gelmetti and Fagnani in EP 2 168 706 propose a flexible rubber retainer to smoothly control the wire payout but their retainer is quite expensive to build as it requires an outer periferical support frame and it is not designed to control aluminium welding wire since it features a plurality of flexible flaps which are freely hanging and pushed downwardly by the force of gravity into the middle of the pack. A soft aluminium wire would have to overcome the resistance of these flaps to be paid out, and that would also inevitably contribute to cause wire deformation. The flaps, in this invention, seem to be aimed at preventing possible tangles caused by the simultaneous feeding of multiple wire strands.
While the first two prior art documents are expressly directed to resolve the problem of the wire deformation, the latter two attempt to rather address the issue of wire tangling during payout from the bulk container.
Gelmetti in U.S. patent application Ser. No. 13/330,314 and International Patent Application PCT/EP2012/076081 teaches of a dynamic retainer to pay wires out of a bulk container such retainer being composed by the assembly of several individual “tiles” connected together but independently raising at the passage of wire. Notwithstanding the dynamic interaction of this retainer with the wire the tiles are rigid pieces and testing has demonstrated that deformation of softer aluminium wires can in fact still occur.
There is a need for a retainer which allows a smooth pay-out of soft, deformable welding wire such as aluminum welding wire.